Crosstalk elimination in the detection of dual-beam optical tweezers by spatial filtering

Comparison of the human's and camel's red blood cell deformability by optical tweezers and Raman spectroscopy

Red blood cells of vertebrates have undergone evolutionary changes over time, leading to the diversification of morphological and mechanical properties of red blood cells (RBCs). Among the vertebrates, camelids have the most different RBC characteristics. As a result of adaptation to the desert environment, camelid RBCs can expand twice as much of their total volume in the case of rapid hydration yet are almost undeformable under mechanical stress. In this work, the mechanical and chemical differences in the RBC properties of the human and camelid species were examined using optical tweezers and Raman spectroscopy. We measured the deformability of camel and human RBCs at the single-cell level using optical tweezers. We found that the deformability index (DI) of the camel and the human RBCs were 0.024 ± 0.019 and 0.215 ± 0.061, respectively. To investigate the chemical properties of these cells, we measured the Raman spectra of the whole blood samples. The result of our study indicated that some of the Raman peaks observed on the camel's blood spectrum were absent in the human blood's spectrum, which further points to the difference in chemical contents of these two species' RBCs.

Basement membrane stiffness determines metastases formation

The basement membrane (BM) is a special type of extracellular matrix and presents the major barrier cancer cells have to overcome multiple times to form metastases. Here we show that BM stiffness is a major determinant of metastases formation in several tissues and identify netrin-4 (Net4) as a key regulator of BM stiffness. Mechanistically, our biophysical and functional analyses in combination with mathematical simulations show that Net4 softens the mechanical properties of native BMs by opening laminin node complexes, decreasing cancer cell potential to transmigrate this barrier despite creating bigger pores. Our results therefore reveal that BM stiffness is dominant over pore size, and that the mechanical properties of 'normal' BMs determine metastases formation and patient survival independent of cancer-mediated alterations. Thus, identifying individual Net4 protein levels within native BMs in major metastatic organs may have the potential to define patient survival even before tumour formation. The ratio of Net4 to laminin molecules determines BM stiffness, such that the more Net4, the softer the BM, thereby decreasing cancer cell invasion activity.

Cancer cells' ability to mechanically adjust to extracellular matrix stiffness correlates with their invasive potential

Increased tissue stiffness is a classic characteristic of solid tumors. One of the major contributing factors is increased density of collagen fibers in the extracellular matrix (ECM). Here, we investigate how cancer cells biomechanically interact with and respond to the stiffness of the ECM. Probing the adaptability of cancer cells to altered ECM stiffness using optical tweezers-based microrheology and deformability cytometry, we find that only malignant cancer cells have the ability to adjust to collagen matrices of different densities. Employing microrheology on the biologically relevant spheroid invasion assay, we can furthermore demonstrate that, even within a cluster of cells of similar origin, there are differences in the intracellular biomechanical properties dependent on the cells' invasive behavior. We reveal a consistent increase of viscosity in cancer cells leading the invasion into the collagen matrices in comparison with cancer cells following in the stalk or remaining in the center of the spheroid. We hypothesize that this differential viscoelasticity might facilitate spheroid tip invasion through a dense matrix. These findings highlight the importance of the biomechanical interplay between cells and their microenvironment for tumor progression.

Optical Trapping of Gold Nanoparticles in Air

Most progress on optical nanoparticle control has been in liquids, while optical control in air has proven more challenging. By utilizing an air chamber designed to have a minimum of turbulence and a single laser beam with a minimum of aberration, we trapped individual 200 to 80 nm gold nanoparticles in air and quantified the corresponding trapping strengths. These results pave the way for construction of metallic nanostructures in air away from surfaces.

Simultaneous three-dimensional tracking of individual signals from multi-trap optical tweezers using fast and accurate photodiode detection

Multiple-beam optical traps facilitate advanced trapping geometries and exciting discoveries. However, the increased manipulation capabilities come at the price of more challenging position and force detection. Due to unrivaled bandwidth and resolution, photodiode based detection is preferred over camera based detection in most single/dual-beam optical traps assays. However, it has not been trivial to implement photodiode based detection for multiple-beam optical traps. Here, we present a simple and efficient method based on spatial filtering for parallel photodiode detection of multiple traps. The technique enables fast and accurate 3D force and distance detection of multiple objects simultaneously manipulated by multiple-beam optical tweezers.